The countries that raised the concerns included France, Italy, Hungary and Slovakia, the people said. Spokespeople for those countries did not respond to POLITICO’s requests for comment. Neither did the Commission.

The warning reflects growing unease around the security of the EU’s supply of petroleum and petroleum derivatives that once flowed through the strait, which includes 40 percent of its jet fuel and diesel imports. The airplane industry is particularly concerned, with Ryanair CEO Michael O’Leary warning that his airline could cancel up to 10 percent of flights through May, June and July if the war continues deep into the summer.

While the EU imports relatively little crude oil from the strait, over 95 percent of the oil the bloc imports comes from abroad. That could further limit refineries’ access to oil as increasing global competition for the fossil fuel tightens supply and raises prices — particularly in countries most exposed to the Gulf, which include Poland, Italy, Greece, the Netherlands, Lithuania, Bulgaria and France, according to data from trade intelligence firm Kpler. According to one national official, some multinational refineries with operations in exposed countries  are already “struggling.”

Asian refineries have already cut their processing by 2.7 million barrels a day since March, the International Energy Agency said in its monthly oil market report, published Tuesday.

While European refineries have yet to publicly broadcast operational difficulties of their own, “if the situation goes on for a few more weeks we’ll get there, because the Asians will be scrambling for physical barrels wherever they come from, and that means they will be less available for Europeans,” said Homayoun Falakshahi, an oil analyst at Kpler.

“If the war continues, and if the Strait of Hormuz isn’t reopened, definitely it will happen, it’s a question of when if not if.”